A method and system for predicting the flow rate of fuel atomizing nozzles for aircraft engines.

Abstract

This invention discloses a method and system for predicting the flow rate of a fuel atomizing nozzle for an aero-engine. The method includes: determining the dimensional parameters of key components based on a three-dimensional geometric model of the fuel nozzle; meshing the three-dimensional geometric model to construct a numerical mesh model of the fuel nozzle; constructing a physical model of fuel flow within the nozzle; using numerical simulation to discretize and solve the physical model based on the numerical mesh model to obtain the liquid pressure drop, the flow rate of the main fuel line bottom cup, the flow rate of the main fuel line nozzle, and the flow rate of the auxiliary fuel line nozzle; calculating the drag loss based on the pressure drop and the drag loss coefficient; calculating the pressure loss coefficient margin; and calculating the flow rate of the fuel atomizing nozzle based on the pressure drop, the drag loss coefficient, and the pressure loss coefficient margin. This invention achieves accurate and stable calculation of nozzle flow rate through two approaches: importing an external geometric model for numerical simulation calculation and directly using a theoretical prediction model.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, and in particular to a method and system for predicting the flow rate of an aero-engine fuel atomizing nozzle. Background Technology

[0002] As a component responsible for fuel injection and atomization, the fuel nozzle's atomization performance significantly impacts engine combustion and stable operation. Flow characteristics are a key focus in fuel atomizing nozzle research. However, due to their small size and complex internal flow, even minute changes in size and surface gloss can affect atomization performance. Furthermore, the geometric dimensions of the nozzle interact with each other, making the study of their flow characteristics a persistent challenge for designers.

[0003] Currently, there are generally two methods for calculating the fuel nozzle flow rate in the combustion chamber of an aero-engine:

[0004] The first method is to use empirical or semi-empirical formulas obtained based on experiments for calculation; the second method is the numerical simulation calculation method that has emerged with the development of modern fluid mechanics, which can simulate the flow of fuel inside the nozzle more realistically and with higher accuracy.

[0005] For the first empirical calculation method, since the prediction model is obtained through experiments, and with any current processing method, processing errors are inevitable, it is difficult to obtain error-free experimental results directly after processing according to the drawing. This leads to a certain gap between the calculated results and the actual situation in the design calculation. Therefore, it is difficult to accurately calculate the flow characteristics of fuel in the nozzle using empirical calculation methods.

[0006] For the second type of numerical simulation, existing methods mainly rely on modules within commercial software for simulation calculations. There is currently no dedicated predictive system or tool for the flow characteristics of fuel nozzles in aero-engine combustion chambers. When using this method to study the variation of flow characteristics of nozzles with different geometric dimensions, it is necessary to construct separate geometric and numerical mesh models for each nozzle type, and finally perform numerical simulation calculations to summarize the patterns and analyze the mechanisms. This process is time-consuming and has significant limitations. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method and system for predicting the flow rate of fuel atomizing nozzles for aircraft engines.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] A method for predicting the flow rate of a fuel atomizing nozzle for an aircraft engine, comprising:

[0010] The dimensional parameters of key components are determined based on the three-dimensional geometric model of the fuel injector; the key components include the main fuel line bottom cup, the main fuel line nozzle orifice, and the auxiliary fuel line nozzle orifice.

[0011] The three-dimensional geometric model is meshed to construct a numerical mesh model of the fuel nozzle;

[0012] Construct a physical model of fuel flow within the nozzle;

[0013] Based on the numerical grid model, the physical model is discretized and solved using numerical simulation methods to obtain the liquid pressure drop, the flow rate of the bottom cup of the main oil circuit, the flow rate of the nozzle of the main oil circuit, and the flow rate of the nozzle of the auxiliary oil circuit.

[0014] The resistance loss of the fuel injector is calculated based on the pressure drop, and the resistance loss coefficient is calculated based on the resistance loss.

[0015] The pressure loss coefficient margin is calculated based on the liquid pressure drop, the flow rate of the main oil circuit bottom cup, the flow rate of the main oil circuit nozzle, the flow rate of the auxiliary oil circuit nozzle, and the dimensional parameters. The pressure loss coefficient margin includes the local pressure loss coefficient margin at the center hole of the main oil circuit bottom cup, the local pressure loss coefficient margin at the front outlet of the main oil circuit nozzle, and the local pressure loss coefficient margin at the front outlet of the auxiliary oil circuit nozzle.

[0016] The flow rate of the fuel atomizing nozzle is calculated based on the pressure drop, the resistance loss coefficient, and the pressure loss coefficient margin.

[0017] Optionally, calculating the flow rate of the fuel atomizing nozzle based on the pressure drop, the drag loss coefficient, and the pressure loss coefficient margin specifically includes:

[0018] The fuel flow velocity is calculated based on the pressure drop, the drag loss coefficient, and the pressure loss coefficient margin.

[0019] The flow rate of the fuel atomizing nozzle is calculated based on the fuel flow velocity.

[0020] Optionally, in the process of constructing the physical model, the Navier-Stokes equations are used to describe the actual flow of fuel in the nozzle, and the RNG k-ε turbulence model is used to describe the turbulence behavior of fuel flowing in the nozzle.

[0021] Optionally, the friction loss h along the straight pipe f1 The calculation formula is as follows:

[0022]

[0023] Where λ is the friction coefficient, d is the straight pipe diameter, u is the fuel flow velocity, and l is the straight pipe length.

[0024] Optionally, the local resistance loss h f2 The calculation formula is or Where u is the fuel flow rate. λ is the local resistance coefficient, d is the friction coefficient, and l is the diameter of the straight pipe. e This is the equivalent length of the pipe or valve.

[0025] Optionally, the formula for calculating the local pressure loss coefficient margin ξ1 at the center hole of the main oil circuit bottom cup is as follows:

[0026]

[0027] Where, q v1 Main oil circuit bottom cup flow rate, A hole The cross-sectional area of ​​the center hole of the main oil circuit bottom cup, A in1 Main oil circuit bottom cup inlet section, A out1 Δp1 is the cross-sectional area of ​​the bottom cup outlet of the main oil circuit, Δp1 is the pressure drop at the center hole of the bottom cup of the main oil circuit, and ρ is the density.

[0028] Optionally, the formula for calculating the local pressure loss coefficient margin ξ2 at the outlet of the main oil circuit nozzle is as follows:

[0029]

[0030] Where, q v2 Main nozzle flow rate, A in2 The cross-sectional area of ​​the wide passage before the nozzle outlet in the main oil circuit, A out2 A is the cross-sectional area of ​​the channel outside the nozzle outlet of the main oil circuit. cao2 Δp2 is the cross-sectional area of ​​the inclined groove at the front end of the main oil circuit nozzle, and Δp2 is the pressure drop at the front end of the main oil circuit nozzle.

[0031] Optionally, the formula for calculating the local pressure loss coefficient margin ξ3 at the outlet of the auxiliary oil circuit nozzle is as follows:

[0032]

[0033] Where, q v3 For the secondary nozzle flow rate, A in3 A is the cross-sectional area of ​​the wide channel before the tapered converging tube at the front end of the auxiliary oil line nozzle. cao3 A is the cross-sectional area of ​​the tapered groove at the front end of the auxiliary oil circuit nozzle. out3 Δp3 is the cross-sectional area of ​​the outer annulus at the outlet of the auxiliary oil circuit nozzle. Δp3 is the pressure drop at the outlet of the auxiliary oil circuit nozzle.

[0034] The present invention also provides a flow prediction system for an aircraft engine fuel atomizing nozzle, comprising:

[0035] The dimension parameter determination module is used to determine the dimension parameters of key parts based on the three-dimensional geometric model of the fuel nozzle; the key parts include the main fuel line bottom cup, the main fuel line nozzle orifice, and the auxiliary fuel line nozzle orifice;

[0036] The numerical mesh model construction module is used to perform mesh generation on the three-dimensional geometric model and construct a numerical mesh model of the fuel nozzle.

[0037] The physical model building module is used to build a physical model of fuel flow within the nozzle;

[0038] The discrete solution module is used to perform discrete solution of the physical model based on the numerical grid model using numerical simulation methods to obtain the liquid pressure drop, the flow rate of the bottom cup of the main oil circuit, the flow rate of the nozzle of the main oil circuit and the flow rate of the nozzle of the auxiliary oil circuit.

[0039] The drag loss and drag loss coefficient calculation module is used to calculate the drag loss of the fuel injector based on the pressure drop, and to calculate the drag loss coefficient based on the drag loss.

[0040] The pressure loss coefficient margin calculation module is used to calculate the pressure loss coefficient margin based on the liquid pressure drop, the main oil circuit bottom cup flow rate, the main oil circuit nozzle orifice flow rate, the auxiliary oil circuit nozzle orifice flow rate, and the dimensional parameters; the pressure loss coefficient margin includes the local pressure loss coefficient margin at the center hole of the main oil circuit bottom cup, the local pressure loss coefficient margin at the front end outlet of the main oil circuit nozzle, and the local pressure loss coefficient margin at the front end outlet of the auxiliary oil circuit nozzle.

[0041] The fuel atomizing nozzle flow calculation module is used to calculate the flow rate of the fuel atomizing nozzle based on the pressure drop, the resistance loss coefficient, and the pressure loss coefficient margin.

[0042] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0043] This invention achieves accurate and stable calculation of nozzle flow rate through two approaches: importing external geometric models for numerical simulation and directly using theoretical prediction models. This method features adjustable geometric and computational parameters, offering significant advantages over existing methods in accurately and quickly obtaining the flow characteristics of a series of nozzles, guiding nozzle design, performance verification, and performance adjustment. It also demonstrates good practicality and scalability. Attached Figure Description

[0044] Figure 1 A flowchart of the flow prediction method for aero-engine fuel atomizing nozzles provided by the present invention;

[0045] Figure 2A schematic diagram of the three-dimensional geometric structure of the fuel nozzle provided by the present invention;

[0046] Figure 3 A schematic diagram of the discretization method of the second-order upwind scheme in the spatial domain provided by the present invention;

[0047] Figure 4 A schematic diagram of a one-dimensional mesh provided by the present invention; wherein, (a) is a schematic diagram of the computational mesh surface, and (b) is a schematic diagram of the surface values ​​and node values ​​of the upwind element;

[0048] Figure 5 This is a schematic diagram of the overall software interface provided by the present invention;

[0049] Figure 6 This is a schematic diagram illustrating the import of external input files provided by the present invention;

[0050] Figure 7 This is a schematic diagram of the key dimension input box provided by the present invention. Detailed Implementation

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0052] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] like Figure 1 As shown, the flow prediction method and system for aero-engine fuel atomizing nozzles provided by this invention includes the following steps:

[0054] Step 101: Determine the dimensional parameters of key components based on the three-dimensional geometric model of the fuel injector; the key components include the main fuel line bottom cup, the main fuel line nozzle orifice, and the auxiliary fuel line nozzle orifice.

[0055] Step 102: Mesh the three-dimensional geometric model to construct a numerical mesh model of the fuel nozzle.

[0056] Step 103: Construct a physical model of fuel flow within the nozzle.

[0057] Step 104: Based on the numerical grid model, the physical model is discretized and solved using numerical simulation methods to obtain the liquid pressure drop, the flow rate of the main oil circuit bottom cup, the flow rate of the main oil circuit nozzle, and the flow rate of the auxiliary oil circuit nozzle.

[0058] Step 105: Calculate the resistance loss of the fuel nozzle based on the pressure drop, and calculate the resistance loss coefficient based on the resistance loss.

[0059] Step 106: Calculate the pressure loss coefficient margin based on the liquid pressure drop, the main oil circuit bottom cup flow rate, the main oil circuit nozzle orifice flow rate, the auxiliary oil circuit nozzle orifice flow rate, and the dimensional parameters; the pressure loss coefficient margin includes the local pressure loss coefficient margin at the center hole of the main oil circuit bottom cup, the local pressure loss coefficient margin at the front outlet of the main oil circuit nozzle, and the local pressure loss coefficient margin at the front outlet of the auxiliary oil circuit nozzle.

[0060] Step 107: Calculate the flow rate of the fuel atomizing nozzle based on the pressure drop, the resistance loss coefficient, and the pressure loss coefficient margin.

[0061] Step 102 specifically includes:

[0062] Both the geometric and numerical mesh models of the fuel injector were created using commercial software. Based on the constructed 3D model, the main and auxiliary fuel passages were separated, and the flow field channels were meticulously meshed. The steps are as follows:

[0063] 1) The fuel atomizing nozzle was reconstructed in three dimensions using UG software to obtain a geometric structure that is basically consistent with the actual structure, such as... Figure 2 As shown.

[0064] 2) Based on step 1), Hypermesh is used to mesh the geometry. According to the calculation requirements, the nozzle structure is divided into main and auxiliary oil passages for separate calculation and analysis. Firstly, the main and auxiliary oil passages are disconnected to study the influence of different component sizes on the internal flow characteristics of the nozzle. Secondly, to focus on the internal flow field of the nozzle, after establishing the three-dimensional geometry of the nozzle, the channel portion is specifically extracted, meshed, and used for flow field calculation and analysis. Only the surfaces of the structure that intersect with the flow field channels are used as boundary conditions in the flow field calculation and analysis.

[0065] Step 103 specifically includes:

[0066] After meshing the nozzle structure in step 101, it is necessary to establish the control equations, i.e., the physical model, for the entire flow field. In the next step, the flow field information is discretized into a series of grid nodes in the geometric shape and the control system corresponding to each node using mathematical discretization methods.

[0067] In this step, to accurately describe the flow of fuel inside the nozzle, a physical model is established using the Navier-Stokes equations, the basic principle of which is as follows:

[0068] For a moving fluid element, based on the three conservation laws, by ensuring that the increments of the control volume's mass, momentum, and energy are equal to the net mass, momentum, and energy flowing in through the control surface, a conservation equation is established. Ignoring volume forces (gravity and electromagnetic forces), its vector form in Cartesian coordinates is as follows:

[0069]

[0070] In the formula:

[0071]

[0072] U is a conserved variable, represented by mass density, dynamic density, and energy density, which can be reduced to the total mass, total momentum, and total energy of the control body through integration.

[0073]

[0074] E, F, and G are viscous fluxes, representing the flow of mass, momentum, and energy perpendicularly through the x, y, and z directions. Specifically, they include mass flow rate, momentum in the x, y, and z directions, energy brought by the inflowing mass, work done by pressure, and impulse brought by pressure.

[0075]

[0076]

[0077]

[0078] E V F V G V Viscous flux refers to the flow of mass, momentum, and energy caused by viscosity.

[0079] σ 11 σ 12 σ 13 σ represents the impulse of the viscous flux per unit area along the x-axis in the x, y, and z directions. 21 σ 22 σ 23 σ is the impulse of the viscous flux per unit area flowing through the y-axis in the x, y, and z directions. 31 σ 32 σ 33 Let q be the impulse of the viscous flux per unit area flowing through the z-axis in the x, y, and z directions. x q y q z This indicates the work done on the control volume by the energy input through heat conduction and viscous forces.

[0080] In the above equations, ρ is density, u, v, and ω are velocity vectors in the x, y, and z directions, respectively, T is absolute temperature, P is pressure, e is total energy per unit volume, and k is the total energy per unit volume. λ is the thermal conductivity.

[0081]

[0082] Where: γ is the specific heat ratio.

[0083] The Navier-Stokes (NS) equations can describe turbulence, but their numerical solutions are extremely resource-intensive; therefore, a turbulence model is introduced. To accurately describe fluid flow with high curvature and high strain rates, this invention primarily employs the RNG k-ε turbulence model within the eddy viscosity model. This turbulence model is based on the Reynolds-averaged NS equations. By averaging the NS equations, solving for the average flow significantly simplifies the computation. For large-scale flows, the averaged NS equations are solved, and the fluctuating term, i.e., the Reynolds stress τ, is also addressed. R This allows us to estimate the impact of small-scale fluctuations on large-scale flow without directly solving the Navier-Stokes equations, thus ultimately describing the overall turbulent flow behavior.

[0084] The Navier-Stokes equations after Reynolds averaging are as follows:

[0085]

[0086] τ is the flow stress based on the average velocity. R For Reynolds stress, Here, ρ is the Hamiltonian operator, U is the conserved variable, and p is the pressure.

[0087] The first equation is the continuity equation, and the second equation is the momentum conservation equation after averaging, which is the sum of the time average and the fluctuating value.

[0088] Reynolds stress τ R As a stress generated by pulsation, the viscosity coefficient is defined by analogy to the mean shear stress. It reflects the shear stress generated by the pulsation of turbulent vortices, and is obtained by solving for the eddy viscosity coefficient μ. t This allows us to obtain the relationship between Reynolds stress and flow.

[0089] As fuel is an incompressible fluid, incorporating isotropic stresses into p, the equation becomes:

[0090]

[0091] Since the eddy viscosity coefficient is flow-dependent and differs in both free turbulence and wall turbulence, an additional dissipation rate ε is added, defined as the rate at which the mechanical energy of isotropic small-scale eddies is converted into thermal energy. By solving for k and ε, the distance traveled by the fluid particle before dissipation can be obtained, thereby solving for the eddy viscosity coefficient and the Reynolds stress fluctuation term.

[0092] To obtain the turbulent kinetic energy k and the dissipation rate ε, in this invention, the influence of buoyancy and compressible velocity turbulent fluctuations on the total dissipation rate is not considered, and the equation is written in the following form:

[0093]

[0094]

[0095] In equation k, the turbulent kinetic energy k is treated as a scalar and includes a time derivative term. Convection term diffusion term Energy obtained from large-scale turbulence (turbulent kinetic energy production term G) k Energy dissipation in small-scale pulsations (ρ) ε Similarly, the equation for ε can be derived, where R is an additional term.

[0096] In the formula, C μ , C 2ε a k a ε All are correlation coefficients, derived analytically through RNG theory and experimental results.

[0097] G k : Indicates the generation of turbulent kinetic energy caused by the average velocity gradient;

[0098]

[0099] viscosity coefficient μ in the diffusion term eff Defined as:

[0100] μ eff =μ+μ t (10)

[0101] Where μ is the dynamic viscosity caused by molecular diffusion, which is a physical property parameter.

[0102] μ t It is the eddy viscosity coefficient, which depends on the flow state:

[0103]

[0104] In the dissipation rate equation of the RNG k-ε turbulence model, R on the right-hand side is an additional term, derived through statistical methods of renormalization group theory, which improves the accuracy of high-speed flow. It is defined as follows:

[0105]

[0106] Where η0 and η are correlation coefficients, and η0 is given by the user.

[0107]

[0108]

[0109] Among them, E ij Let this be the tensor of the surface.

[0110] The corresponding coefficients are set as follows:

[0111] C μ =0.0845

[0112] C 1ε =1.42

[0113] C 2ε =1.68

[0114] a k =a ε =1.39

[0115] η0 = 4.377

[0116] β = 0.012

[0117] Step 104 specifically includes:

[0118] After constructing a physical model of fuel flow within the nozzle, numerical methods are needed to discretize the model. This invention selects the finite volume method, which is relatively mature in computational fluid dynamics, for model discretization, including both spatial and temporal discretization.

[0119] Discretization in the spatial domain: Due to the instability of the central difference scheme and the instability and low accuracy of the first-order upwind scheme, and considering the influence of the curvature of the distribution curves between nodes on physical quantities, this invention employs a second-order upwind scheme, a higher-order upwind scheme, for the convection term, such as... Figure 3 As shown, Figure 3 In the middle, V fThe vector representing the center position of the volume element defines the direction of flow. C is the center of the grid element, f represents the center position of the grid surface, D is the center position of the grid element one cell downstream of the current center, and DD is the center position of the grid element two cells downstream of the current center. U is the center position of the grid element one cell upstream of the current center, and UU is the center position of the grid element two cells upstream of the current center. Where φ... C φ D φ DD φ U φ UU These are the general variables corresponding to the grid center, φ f This is the general variable corresponding to the center of the mesh surface.

[0120] In order to obtain an accurate physics analysis, the diffusion term uses a central difference scheme.

[0121] First, for the numerical solution of the one-dimensional convection-diffusion problem, in the mesh, based on the discretization of the continuity equation, the surface integral is replaced by the sum of fluxes on the mesh cell surfaces, resulting in the discrete equation:

[0122]

[0123] In the formula, φ is a generalized variable, i.e., the physical quantity to be determined; Γ is the diffusion coefficient; nb represents adjacent nodes; ρ is the density; and u is the velocity in one-dimensional coordinates. As a unit vector in the x-direction, when generalized to three-dimensional problems, it can be represented by the physical quantity U as velocities u, v, and w; To control the area of ​​the volume interface.

[0124] In terms of the interpolation format, by linear extrapolating the values ​​of the two upstream grid cells, we have:

[0125]

[0126] x f x c x U The coordinates of the node on the x-axis.

[0127] For a uniform grid, it simplifies to:

[0128]

[0129] Taking a one-dimensional mesh as an example, such as Figure 4 As shown. By discretizing the convection term using a second-order upwind scheme and the diffusion term using a central difference scheme, the general scheme is obtained:

[0130] a C φ C =a E φ E +a EE φEE +a W φ W +a WW φ WW (twenty three)

[0131] Figure 4 In (a), C is the center of the grid cell, and e and w are the center positions of the grid surfaces upstream and downstream of the grid cell center. e and S w S is the mesh surface vector of mesh surfaces e and w. e and S w The modulus of the mesh surface vector.

[0132] Figure 4 In (b), WW, W, C, E, and EE are the centers of the grid cells, and φ W φ C φ E φ is a generalized physical quantity (universal variable) at the center of the grid. w φ e This is a general variable representing the center position of the mesh surface. w u ww u e u ee The velocity is at the center of the grid surface.

[0133] In the formula:

[0134]

[0135] Among them: FluxF e FluxF w FluxF ee FluxF ww FluxC f All represent the flow mass flow rate of each control unit; x e x w Let |a,b|| represent the coordinates of the grid nodes on the x-axis, and ||a,b|| represent the maximum value between a and b. and Let be the mass flow rate on surfaces e and w.

[0136] In this invention, the above method is extended to three dimensions for discretization.

[0137] Discretization in the time domain: This invention employs a fully implicit scheme for discretizing the time term (non-steady-state term), and its time step is not limited by computational stability. Its discretization method is similar to that in the spatial domain, transforming the integral over space into an integral over the time domain.

[0138] For transient problems, the governing equations are:

[0139]

[0140] In the formula: ζ(φ) is the time operator, and ζ(φ) is the space operator.

[0141] Taking control unit C and integrating it, we get:

[0142]

[0143] Discretizing the centroid space yields:

[0144]

[0145] in, V is a spatial discrete operator at a certain reference time. C For the control unit volume, ρ c To control the fluid density of the control unit.

[0146] Using the quasi-time element method, the discrete equation is obtained as follows:

[0147]

[0148] Based on the established physical model and numerical simulation method of the fuel nozzle, to obtain the influence of typical dimensions on fuel flow characteristics, numerical simulations were performed on the fuel flow process within the key structures of the main and auxiliary fuel passages. The numerical simulation of the flow field in the key parts was used to understand the pressure drop variation at these critical locations. Then, using the drag loss model established in step 105, the results were inverted and fitted with the calculation results from that step to obtain the drag loss coefficient and the pressure loss coefficient of the entire flow field. The steps are as follows:

[0149] 1) Numerical simulation of fuel flow process within key structures of the auxiliary oil circuit. The results show that the fluid experiences significant friction loss due to the long flow distance. Large pressure drops occur at the valve opening section, the inclined groove, and the minimum outlet of the conical structure.

[0150] Table 1 lists the calculated pressure drop data for the auxiliary oil circuit and valve core.

[0151] Table 1. Dimensional parameters of the inner core of the auxiliary oil circuit valve and the internal structure of the oil pipe, and fluid pressure drop.

[0152]

[0153]

[0154] 2) Numerical simulation of fuel flow process within key structures of the main oil circuit. The numerical simulation results show that the pressure drop mainly occurs downstream of the valve, and the central orifice diameter of the bottom cup is the core factor affecting the fluid pressure drop. The pressure drop is relatively uniform within the main oil circuit, but a larger pressure drop occurs at the point where it enters the vortex channel.

[0155] Table 2 shows the calculated structural dimensions and liquid pressure drop of the main oil circuit valve core and oil pipe.

[0156] Table 2. Dimensional parameters of the inner core of the main oil circuit valve and the internal structure of the oil pipe, and fluid pressure drop.

[0157]

[0158] Specifically, steps 104-107 include:

[0159] Construction and parameter fitting of a theoretical prediction model for flow characteristics within a fuel nozzle

[0160] Step 1: Building the framework of the theoretical prediction model based on the conservation of mechanical energy

[0161] Based on the law of conservation of mechanical energy, a theoretical prediction model framework for the flow characteristics inside a fuel nozzle is established. Due to the viscosity of actual fluids, mechanical energy loss, also known as drag loss h, occurs when internal friction is applied. f When considering this term in the mechanical energy balance between specific cross-sections 1-1 and 2-2, the mechanical energy balance formula can be obtained as follows:

[0162]

[0163] In the formula, h represents the average kinetic energy per unit mass of fluid at a given cross-section, expressed in J / kg. f The mechanical energy loss (i.e., resistance loss) per unit mass of fluid flowing from section 1-1 to section 2-2 is expressed in J / kg.

[0164] In engineering calculations, average velocity is used to express average kinetic energy. Introducing a kinetic energy correction coefficient a, equation (29) can be written as follows:

[0165]

[0166] The correction coefficient 'a' in the formula is related to the shape of the velocity distribution.

[0167] To obtain the drag loss h f The study clarified that the nozzle mainly consists of several parts: a straight pipe and pipe fittings such as elbows, slant grooves, valves, and flow-stopping orifices. The friction loss caused by the straight pipe and the local resistance loss caused by the pipe fittings are essentially due to the viscosity and internal friction of the flowing fluid. The process of determining their specific values ​​will be shown in the following two steps.

[0168] Step 2: Determining the friction loss along the straight pipe:

[0169] In determining the straight pipe resistance, a computational fluid dynamics-based experimental and dimensional analysis method was employed. The general content is as follows:

[0170] Numerical experiments were conducted to identify the main factors affecting fuel flow characteristics.

[0171] A unified expression for straight pipe resistance, whether in laminar or turbulent flow, can be written in a unified form:

[0172]

[0173] In the formula, the friction coefficient λ is a function of the Reynolds number Re and the relative roughness ε / d, that is:

[0174]

[0175] For laminar straight pipe flow with Re < 2000, the friction coefficient is written as:

[0176]

[0177] Studies have shown that the friction coefficient λ in turbulent flow can be calculated using the following formula:

[0178]

[0179] Based on the above theory, in order to obtain the specific resistance coefficient in the nozzle under study more accurately, numerical experiments were conducted by changing the physical property parameters and operating conditions to determine the straight pipe resistance loss h under turbulence. f1 Analysis and preliminary experiments show that the influencing factors are as follows: 1) Physical properties: density and viscosity; Structural factors: pipe diameter, pipe length, and pipe wall roughness; Working conditions: flow velocity inside the pipe.

[0180] 2) Planning numerical experiments.

[0181] To obtain the straight pipe resistance loss h later f1 Depending on the specific changing patterns of the influencing factors, it is necessary to modify one of the independent variables while keeping other independent variables constant for research purposes. To reduce the workload of numerical simulation experiments, this invention employs dimensional analysis, based on the principle that both sides of any physical equation or each term in the equation has the dimension of phase, and plans the number of experiments accordingly.

[0182] 3) Data processing to accurately express experimental results.

[0183] After obtaining the dimensionless number group, through multiple experiments and data processing, the specific functional expression of the straight pipe friction resistance in this type of nozzle was determined.

[0184] Step 3: Determining Local Resistance Loss

[0185] 1) Determine the approximate calculation method for local resistance.

[0186] Regarding local resistance loss, due to its complexity, the wide variety of pipe and valve types and specifications, and the difficulty in precise calculation, this invention uses the following two approximate methods to represent the local resistance loss of key parts:

[0187] a. It is approximately assumed that local resistance loss follows the square law:

[0188]

[0189] In the formula, The local drag coefficient is determined through numerical experiments.

[0190] b. It is approximated that the local resistance loss is equivalent to a straight pipe of a certain length:

[0191]

[0192] In the formula, l e The equivalent length of the pipe fitting is determined through numerical experiments, where d is the straight pipe diameter and u is the fuel flow rate.

[0193] Some commonly used pipe and valve fittings and l e This can be obtained by looking up a table. For sudden expansion and contraction, the velocity u needs to be selected as the average velocity of the small tube cross section.

[0194] 2) Determination of local drag coefficient

[0195] The following set of equations is required to calculate the fuel flow rate within the nozzle:

[0196] mass conservation equation:

[0197]

[0198] q v d represents flow rate, d represents diameter, and u represents fuel flow velocity.

[0199] Mechanical energy balance formula:

[0200]

[0201] P represents pressure, Δp is the pressure difference between inlet and outlet, ρ is density, gz1 and gz2 represent gravitational potential energy, and h f11 h is the sum of friction loss and partial local resistance loss calculated using the friction loss formula. f21ξ represents the partial local resistance loss, and ξ represents the local pressure loss coefficient margin.

[0202] Formula for calculating the coefficient of friction:

[0203]

[0204] In the formula, μ is the fuel dynamic viscosity. This refers to relative roughness.

[0205] Based on the above research methods, the formulas for the local resistance coefficients of several key components studied in this invention are as follows:

[0206] At the bottom cup of the main oil circuit: the local resistance coefficient at this location was determined through literature review and numerical verification. The value: First, the resistance coefficient for the sudden contraction from wide channel 1-1 to narrow channel 2-2. In other words, the formula is:

[0207]

[0208] Where A1 and A2 are the cross-sectional areas of the wide channel and the narrow channel, respectively.

[0209] For the resistance coefficient of the sudden expansion from narrow channel 1-1 to wide channel 2-2, the formula is:

[0210]

[0211] Where A1 and A2 are the cross-sectional areas of the narrow channel and the wide channel, respectively.

[0212] Therefore, for the bottom cup of the main oil passage that expands again from wide channel 1-1 through narrow channel 2-2 to 3-3, the formula for the resistance coefficient is:

[0213]

[0214] A1 corresponds to the cross-sectional area A of the bottom cup inlet of the main oil circuit. in A2 corresponds to the cross-sectional area A of the center hole of the main oil circuit bottom cup. hole A3 is the cross-sectional area of ​​the bottom cup of the main oil circuit, corresponding to A out .

[0215] At the tapered converging tube at the front end of the secondary nozzle; for this structure, the drag coefficient formula from the coarse section 1-1 to the fine section 2-2 is:

[0216]

[0217] Where k is the correlation coefficient determined through numerical simulation, and A1 corresponds to the A1 of the cross-sectional area of ​​the auxiliary oil passage inlet. in A2 is the cross-sectional area A of the secondary nozzle.hole .

[0218] The calculation method for the resistance coefficient of the material entering the inclined channel from the wide channel and then flowing out of the inclined channel into the annular channel is the same as that of formula (42).

[0219] Step 4: Determination of the final formula of the theoretical prediction model for fuel nozzle flow characteristics

[0220] As can be seen from formula (38), based on obtaining the formulas for each drag coefficient, the obtained friction loss is combined with the sum of local drag h, which is partially approximated by the friction loss calculation formula. f11 With partial local resistance loss h f21 Substitute the values ​​into the equations and use numerical simulation to determine the unknowns (such as correlation coefficient k, velocity u, etc.). Since there is pressure loss when the medium is being transported, after determining the margin of each pressure loss coefficient, the relationship between the flow rate of fuel in the nozzle and the corresponding dimensional parameters can be obtained, i.e. (46)-(48).

[0221] For the key components studied in this invention, numerical simulation was used for calculation and analysis. Data inversion and parameter fitting were performed on the unknown parameters (flow rate, pressure drop, and dimensional parameters), and the determined parameters include:

[0222] The calculation formula for the main oil passage inclined groove is as follows:

[0223] A cao2 =4.0*L cao2 *(-2943.7*L cao2 *L cao2 +10.606*L cao2 -0.0088) / 0.00078*H cao2 (44)

[0224] A cao2 The cross-sectional area of ​​the inclined groove at the front end of the main oil circuit nozzle, L cao2 Inclined groove width, H cao2 This is the height of the inclined groove.

[0225] The calculation formula for the auxiliary oil passage inclined groove is:

[0226] A cao3 =4.0*L cao3 *H cao3 (45)

[0227] Pressure loss coefficient margin calculation:

[0228] The formula for calculating the local pressure loss coefficient margin ξ1 at the center hole of the main oil circuit bottom cup is:

[0229]

[0230] Where, q v1 The flow rate of the main oil circuit bottom cup is Δp1, the pressure drop of the main oil circuit bottom cup center hole is ρ, and A is the density. cao1 Main oil passage inclined groove cross-sectional area, L cao1 Main oil passage inclined groove width, H cao1 Main oil passage inclined groove height, A hole1 The cross-sectional area of ​​the center hole of the main oil circuit bottom cup.

[0231] The formula for calculating the local pressure loss coefficient margin ξ2 at the outlet of the main oil circuit nozzle is as follows:

[0232]

[0233] Where, q v2 Main nozzle flow rate, A in2 The cross-sectional area of ​​the wide passage before the nozzle outlet in the main oil circuit, A out2 A is the cross-sectional area of ​​the channel outside the nozzle outlet of the main oil circuit. cao2 Δp2 is the cross-sectional area of ​​the inclined groove at the front end of the main oil circuit nozzle, and Δp2 is the pressure drop at the front end of the main oil circuit nozzle.

[0234] The formula for calculating the local pressure loss coefficient margin ξ3 at the outlet of the auxiliary oil circuit nozzle is as follows:

[0235]

[0236] Where, q v3 For the secondary nozzle flow rate, A in3 A is the cross-sectional area of ​​the wide channel before the tapered converging tube at the front end of the auxiliary oil line nozzle. cao3 A is the cross-sectional area of ​​the tapered groove at the front end of the auxiliary oil circuit nozzle. out3 Δp3 is the cross-sectional area of ​​the outer annulus at the outlet of the auxiliary oil circuit nozzle. Δp3 is the pressure drop at the outlet of the auxiliary oil circuit nozzle.

[0237] Next, using the above method, the local pressure loss coefficient margins of all key parts of the nozzle and the margins of all friction pressure loss coefficients are further obtained. Then, using formulas (38) and (39), the nozzle pressure drop, all local and friction pressure loss coefficient margins, various dimensional parameters, and loss coefficients are substituted to establish the flow prediction model of the entire fuel nozzle. The formula is as follows:

[0238]

[0239] Among them, A in The total nozzle inlet cross-sectional area, A out λ is the total nozzle outlet cross-sectional area. tube l is the friction loss coefficient along the pipeline. tube Let d be the length of the oil pipe.tube The diameter of the oil pipe. ξ4 is the local resistance loss coefficient of the main and auxiliary valve cores and other parts, ξ5 is the pressure loss coefficient margin of the main and auxiliary valve cores and other parts, A4 is the cross-sectional area of ​​the narrow channel of the main and auxiliary valve cores and other parts. All the above parameters are determined by numerical simulation and are constant values.

[0240] This invention also includes a nozzle fluid simulation software system, the specific process of which is as follows:

[0241] The software system was developed using Qt. For the fuel flow performance simulation software to be developed, a software functional requirements framework was built based on the simulation process and functional requirements. To achieve the desired objectives, this software system integrates two functions: simulation calculation and result post-processing. The main modules of the software include geometric data import, calculation parameter setting, background program solution calculation, and interface display. These modules correspond to the main steps of the simulation calculation.

[0242] The following sections will introduce the three parts of the software architecture: 1) the integration of the atomization performance calculation program and software; 2) the transformation of the functional requirements framework into the software architecture; and 3) the functions of the project files and the functions of data display settings.

[0243] 1) Integration of atomization performance calculation program and software

[0244] Regarding the software architecture, this invention first considers the integration of the atomization performance calculation program and the software. The atomization performance calculation program developed in this invention is a C++ console program. The structured data input program reads the text file "XXX.EXL". The results are output either as a text file or displayed via a user interface. In terms of integrating the atomization performance program and the software, this invention embeds the program's code into the software code, merging the software code and the simulation solution code into a single codebase, which is then compiled into a single software program.

[0245] 2) Transformation of functional requirements framework into software architecture

[0246] Starting with the four main functional modules in the software functional requirements framework, this paper further analyzes how the functional requirements of each module are implemented in the software, and constructs the architecture of each module:

[0247] ① Reading geometric parameter files

[0248] ② Calculation parameter settings.

[0249] ③ Simulation solution calculation

[0250] ④ Post-processing

[0251] 3) Project file functions and data display functions

[0252] This software, titled "Fuel Atomizing Nozzle Flow Calculation Software," consists of two main parts, and its interface is shown below. Figure 5 .

[0253] The left half of the software mainly consists of the main and auxiliary oil circuit reference model module for the nozzle, as well as the nozzle model and spray process display module.

[0254] The main and auxiliary oil circuit reference models include the main oil circuit bottom cup model, the main oil circuit nozzle front end model, and the auxiliary oil circuit nozzle front end model. All key dimensional parameters required for calculation are marked in the reference models, allowing users to more clearly understand the meaning of each key dimensional parameter in the oil circuit.

[0255] The module in the lower right corner displays the nozzle model and spray process. When different oil circuits are used, this module will show the corresponding oil circuit liquid film animation, allowing users to more intuitively understand the nozzle spray process of different oil circuits.

[0256] The right half of the software mainly displays calculation parameters and results. Calculation parameter settings include general parameter settings and key oil circuit dimensions settings. The general parameter settings module includes inlet pressure Pin, outlet pressure Pout, and fuel density Rho. Users can enter the required parameters in the input boxes to the left of these parameters.

[0257] The system includes two modules for setting key dimensions in the main and auxiliary oil circuits, allowing users to configure specific key dimensions for each circuit. There are two methods for setting key dimensions: one is by importing an external input file. When "Yes" is selected, an add file window will pop up, allowing the user to add the required input file. In this case, the key dimension input box will be hidden, and parameter settings will not be possible. Figure 6 As shown.

[0258] Secondly, input is done through the corresponding input box. This method is the default input method or is selected when clicking "No," such as... Figure 7 As shown.

[0259] When you click on "Calculate", the oil circuit working flow rate will be displayed in the display box on the right.

[0260] The main and auxiliary oil circuits can be calculated individually or simultaneously. Calculating the main oil circuit's operating flow rate requires setting general parameters and key dimensions; calculating the auxiliary oil circuit's operating flow rate also requires setting general parameters and key dimensions; calculating the flow rate when both main and auxiliary oil circuits are operating simultaneously requires setting general parameters and all key dimensions for both main and auxiliary oil circuits. The general parameters are applicable to all three calculation modes and can be set once without modification.

[0261] The present invention has the following advantages:

[0262] (1) It has good systematicity: Traditional nozzle design methods rely heavily on commercial software and lack systematicity and scalability, sometimes requiring the use of multiple software programs. On the other hand, when performing nozzle calculations, the calculation cycle is very long in order to obtain accurate results, and multiple numerical simulation calculations are often required during later modifications. This invention combines the advantages of numerical simulation and theoretical prediction methods, creatively developing a system that integrates both calculation methods, and adding post-processing functions.

[0263] (2) High accuracy: Traditional methods for calculating fuel nozzle flow rate are based on experimentally obtained coefficient curves and empirical formulas, which have certain discrepancies with the actual fuel flow characteristics. This invention uses numerical simulation and dimensional analysis to obtain a theoretical prediction model for fuel flow rate, thus solving the problem of inaccuracy in models obtained through experiments.

[0264] The present invention also provides a flow prediction system for an aircraft engine fuel atomizing nozzle, comprising:

[0265] The numerical mesh model building module is used to build a numerical mesh model of the fuel nozzle.

[0266] The physical model building module is used to build a physical model of fuel flow within the nozzle;

[0267] The module for determining size parameters and liquid pressure drop is used to discretize the physical model based on the numerical grid model using numerical simulation methods to determine the size parameters and liquid pressure drop of key components; the key components include the main oil circuit bottom cup, the main oil circuit nozzle orifice, and the auxiliary oil circuit nozzle orifice.

[0268] The resistance loss calculation module is used to calculate the resistance loss of the fuel nozzle based on the dimensional parameters and the liquid pressure drop; the resistance loss includes straight pipe friction loss and local resistance loss;

[0269] The fuel nozzle flow calculation module is used to calculate the flow rate of the fuel nozzle based on the resistance loss coefficient and the resistance loss; the fuel nozzle flow rate includes the main fuel line bottom cup flow rate, the main nozzle flow rate, and the auxiliary nozzle flow rate.

[0270] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0271] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for predicting the flow rate of a fuel atomizing nozzle for an aircraft engine, characterized in that, include: The dimensional parameters of key components are determined based on the three-dimensional geometric model of the fuel injector; the key components include the main fuel line bottom cup, the main fuel line nozzle orifice, and the auxiliary fuel line nozzle orifice. The three-dimensional geometric model is meshed to construct a numerical mesh model of the fuel nozzle; Construct a physical model of fuel flow within the nozzle; Based on the numerical grid model, the physical model is discretized and solved using numerical simulation methods to obtain the liquid pressure drop, the flow rate of the bottom cup of the main oil circuit, the flow rate of the nozzle of the main oil circuit, and the flow rate of the nozzle of the auxiliary oil circuit. The resistance loss of the fuel nozzle is calculated based on the pressure drop, and the resistance loss coefficient is calculated based on the resistance loss; the resistance loss includes straight pipe friction loss and local resistance loss. The pressure loss coefficient margin is calculated based on the liquid pressure drop, the flow rate of the main oil circuit bottom cup, the flow rate of the main oil circuit nozzle, the flow rate of the auxiliary oil circuit nozzle, and the dimensional parameters. The pressure loss coefficient margin includes the local pressure loss coefficient margin at the center hole of the main oil circuit bottom cup, the local pressure loss coefficient margin at the front outlet of the main oil circuit nozzle, and the local pressure loss coefficient margin at the front outlet of the auxiliary oil circuit nozzle. The flow rate of the fuel atomizing nozzle is calculated based on the pressure drop, the drag loss coefficient, and the pressure loss coefficient margin. The formula for calculating the local pressure loss coefficient margin ξ1 at the center hole of the main oil circuit bottom cup is as follows: Where, q v1 Main oil circuit bottom cup flow rate, A hole The cross-sectional area of ​​the center hole of the main oil circuit bottom cup, A in1 Main oil circuit bottom cup inlet section, A out1 Δp1 is the cross-sectional area of ​​the main oil circuit bottom cup outlet, Δp1 is the pressure drop at the center hole of the main oil circuit bottom cup, and ρ is the density. The formula for calculating the local pressure loss coefficient margin ξ2 at the outlet of the main oil circuit nozzle is as follows: Where, q v2 Main nozzle flow rate, A in2 The cross-sectional area of ​​the wide passage before the nozzle outlet in the main oil circuit, A out2 A is the cross-sectional area of ​​the channel outside the nozzle outlet of the main oil circuit. cao2 Δp2 is the cross-sectional area of ​​the inclined groove at the front end of the main oil circuit nozzle, and Δp2 is the pressure drop at the front end of the main oil circuit nozzle. The formula for calculating the local pressure loss coefficient margin ξ3 at the outlet of the auxiliary oil circuit nozzle is as follows: Where, q v3 For the secondary nozzle flow rate, A in3 A is the cross-sectional area of ​​the wide channel before the tapered converging tube at the front end of the auxiliary oil line nozzle. cao3 A is the cross-sectional area of ​​the tapered groove at the front end of the auxiliary oil circuit nozzle. out3 Δp3 is the cross-sectional area of ​​the outer ring at the front outlet of the auxiliary oil circuit nozzle, and Δp3 is the pressure drop at the front outlet of the auxiliary oil circuit nozzle.

2. The flow rate prediction method for aero-engine fuel atomizing nozzles according to claim 1, characterized in that, The calculation of the fuel atomizing nozzle flow rate based on the pressure drop, the drag loss coefficient, and the pressure loss coefficient margin specifically includes: The fuel flow velocity is calculated based on the pressure drop, the drag loss coefficient, and the pressure loss coefficient margin. The flow rate of the fuel atomizing nozzle is calculated based on the fuel flow velocity.

3. The flow rate prediction method for aero-engine fuel atomizing nozzles according to claim 1, characterized in that, In the process of constructing the physical model, the Navier-Stokes equations are used to describe the actual flow of fuel in the nozzle, and the RNG k-ε turbulence model is used to describe the turbulence behavior of fuel flowing in the nozzle.

4. The flow rate prediction method for aero-engine fuel atomizing nozzles according to claim 1, characterized in that, The friction loss along the straight pipe h f1 The calculation formula is as follows: Where λ is the friction coefficient, d is the straight pipe diameter, u is the fuel flow velocity, and l is the straight pipe length.

5. The flow rate prediction method for aero-engine fuel atomizing nozzles according to claim 1, characterized in that, The local resistance loss h f2 The calculation formula is or Where u is the fuel flow rate. λ is the local resistance coefficient, d is the friction coefficient, and l is the diameter of the straight pipe. e This is the equivalent length of the pipe or valve.

6. A flow prediction system for an aircraft engine fuel atomizing nozzle, characterized in that, The flow prediction system is applied to the flow prediction method for the fuel atomizing nozzle of an aero-engine according to any one of claims 1-5, and the flow prediction system comprises: The dimension parameter determination module is used to determine the dimension parameters of key parts based on the three-dimensional geometric model of the fuel nozzle; the key parts include the main fuel line bottom cup, the main fuel line nozzle orifice, and the auxiliary fuel line nozzle orifice; The numerical mesh model construction module is used to perform mesh generation on the three-dimensional geometric model and construct a numerical mesh model of the fuel nozzle. The physical model building module is used to build a physical model of fuel flow within the nozzle; The discrete solution module is used to perform discrete solution of the physical model based on the numerical grid model using numerical simulation methods to obtain the liquid pressure drop, the flow rate of the bottom cup of the main oil circuit, the flow rate of the nozzle of the main oil circuit and the flow rate of the nozzle of the auxiliary oil circuit. The resistance loss and resistance loss coefficient calculation module is used to calculate the resistance loss of the fuel injector based on the pressure drop, and to calculate the resistance loss coefficient based on the resistance loss; the resistance loss includes straight pipe friction loss and local resistance loss; The pressure loss coefficient margin calculation module is used to calculate the pressure loss coefficient margin based on the liquid pressure drop, the main oil circuit bottom cup flow rate, the main oil circuit nozzle orifice flow rate, the auxiliary oil circuit nozzle orifice flow rate, and the dimensional parameters; the pressure loss coefficient margin includes the local pressure loss coefficient margin at the center hole of the main oil circuit bottom cup, the local pressure loss coefficient margin at the front end outlet of the main oil circuit nozzle, and the local pressure loss coefficient margin at the front end outlet of the auxiliary oil circuit nozzle. The fuel atomizing nozzle flow calculation module is used to calculate the flow rate of the fuel atomizing nozzle based on the pressure drop, the resistance loss coefficient, and the pressure loss coefficient margin.

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